DESCRIPTION: Studies on human color vision are proposed with a specific focus on the distribution of the different cone types in the human retina and the nature of their contributions to color appearance. Psychophysical techniques and a model of small spot detection have been used to assay the relative numbers of L and M cones in the living human eye. From the current sample of twelve eyes, it was concluded that the relative numbers of L to M cones is roughly two, with a range between 1.3 and 2.5. The relative numbers of L and M cones remains constant from 28 deg temporal to 28 deg nasal along the horizontal meridian. It is concluded that the relative numbers of L and M cones can be linked directly to color perception at the opponent level by showing that an individual's L to M cone ratio predicts the wavelength seen as unique yellow in the fovea centralis and in the periphery. Building on this work the following goals are proposed: (1) The topographical arrangement of the L and M cone populations in the peripheral retina will be measured using a small spot probe (illuminating one or a few cones) and a color naming procedure. (2) The topographical arrangement of the L and M cones in the fovea will be assessed using a hyperacuity task. The hyperacuity task was chosen to circumvent the tight packing of foveal cones which precludes illumination of single foveal cones in the human eye. (3) An ideal observer model will be developed and an optimization technique will be designed to select the underlying cone mosaic most likely to produce the psychophysical results such as color naming (Aim 1) and hyperacuity (Aim 2). (4) These approaches will be used to map the locations of S cones in the living human eye. Although others have mapped the locations of S cones, this method provides an independent analysis and allows full pursuit of Aim 5. (5) The objective here is to provide a full account of the opponent site in terms of the contributions of L, M, and S cones. Prior work from this laboratory provided such a specification for the mid-to long wavelength ranges of the red/green system. This will be extended to include a complete description for the short-wavelength ranges of the red/green system, involving the S cones. Additional experiments are proposed aimed at defining the inputs of the L, M and S cones to the yellow/blue system.